If a single journey across London requires one or bus transfers, will the driver give me a transfer coupon or???
There are no transfer tickets on London buses. Unless you get a bus pass or Travelcard, you will have to buy a new ticket or pay with your Oyster card every time you change buses. Also, remember that buses in central London no longer sell tickets from the driver - if you don't have an Oyster card you need to buy tickets from coin-operated machines at stops which can be unreliable.
What Phillip from the Big Smoke said is bang on. Remember that Oyster cards cap out at less than a Travelcard. If you use only buses your cap is lower than if you use a mixture of tubes and buses. Every bus, another charge.